1. Field of the Invention
This invention relates to a motion compensator to be placed in a well pipe to permit relative movement between an underwater well installation and a floating vessel on the water surface. The motion compensator is particularly useable while conducting a production test of an underwater well. Additionally, the invention relates to a method for using the motion compensator.
2. The Prior Art
Motion compensators to permit relative movement between an underwater well installation and a floating vessel are well known.
Motion compensators may take the form of an inner-sleeve telescopable within an outer barrel with seal means disposed between the sleeve and barrel as illustrated in U.S. Pat. Nos: to McNeill 2,606,003; Kofahl 3,179,179; Lacy 3,211,224; and Walker 3,329,221.
Motion compensators may be utilized in a well drill string as illustrated by U.S. Pat. Nos: to Ware 3,194,330; Slator et al 3,599,735; and Kisling III et al 3,764,168 or in a well test string as illustrated by U.S. Pat. Nos. to Hyde 3,354,950; Young et al 3,741,305; Manes et al 3,646,995; Kisling III 3,643,505; and Nutter 3,823,773.
A pressure balanced motion compensator, wherein the forces due to well fluid pressure tending to expand the compensator are balanced by the forces due to well fluid pressure tending to contract the compensator, is disclosed in U.S. Pat. No. 3,354,950 to Hyde.
Splines on a motion compensator to permit the transmission of torque through the motion compensator are disclosed in U.S. Pat. Nos. 2,606,003; 3,194,330 and 3,354,950.
One persistent problem with motion compensators has been seal failure. As the floating vessel oscillates due to wave action, telescoping elements of the motion compensator move relative to each other to accommodate the oscillation. During the telescoping action, the seal surfaces are exposed to well fluids. The fluids contain abrasive particles. The particles tear up the seals and contribute to seal failure.
Various attempts have been made to prolong seal life and thereby provide a motion compensator that can be used longer. U.S. patent to Hanes et al U.S. Pat. No. 3,647,245 discloses a telescoping pipe joint wherein the seal assembly is impregnated with a lubricant before the joint is positioned within the well pipe. The aforementioned patent to Slator et al U.S. Pat. No. 3,599,735 discloses a telescoping pipe joint wherein, before the joint is positioned within the well pipe, an annular cavity between two seal assemblies is filled with lubricant. The aforementioned patent to Kisling III et al, U.S. Pat. No. 3,764,168 includes a seal tube to isolate the seal wear surface on the telescoping element from well fluids.
However, present motion compensators do not have a sufficient life span for some operations presently being contemplated for offshore wells. Present well tests from floating vessels generally last for 4 hours, however, comtemplated production tests are expected to last from 12 to 36 hours. The telescoping elements of a motion compensator utilized during such a production test would undergo much more relative movement than is undergone by the elements of present motion compensators. With more relative movement the likelihood of seal failure increases and there is a corresponding increase in the desire to lengthen seal life by reducing seal wear.
A motion compensator, as disclosed and claimed in the copending application of George M. Raulins entitled Motion Compensator now issued as U.S. Pat. No. 4,072,190 is generally satisfactory in providing protection to seals in a motion compensator to prolong their life.
However, even with the best constructed motion compensator and even with protection provided to the seals, seals will fail. When the seals fail, well fluids can escape from the interior of the compensator to the exterior causing environmental damage, loss of well fluids, and perhaps even loss of well equipment and personnel. This application discloses and claims an improvement over the aforementioned, copending application of George M. Raulins, and it is an object of this invention to provide a motion compensator which has means for detecting environmental seal failure.
Another object of this invention is to provide a motion compensator including means for monitoring its environmental seals so that the condition of the environmental seals during the operation of the motion compensator will be known.
Another object of this invention is to provide a motion compensator having a pair of seals to prevent loss of fluids to the environment with a primary seal designed to be the first to fail and the life of the second back up seal being estimatable.
Another object of this invention is to provide a pressure balanced motion compensator including pressure balancing seals and a pair of seals to prevent loss of fluids to the environment which can be operated while maintaining the pressure balancing feature and preventing loss of fluid to the environment when all but the back up environmental seal have experienced some degree of failure.
Another object of this invention is to provide a method of operating a motion compensator in a manner to detect seal failure of the environmental primary seal.
Another object of this invention is to provide a method of operating a motion compensator having a pair of seals to protect loss of fluids to the environment to determine when the primary environmental seal fails and to estimate the life of the back up environmental seal.
Another object of this invention is to provide a method of operating a pressure balanced motion compensator including pressure balancing seals and a pair of seals to prevent loss of fluids to the environment which permits accommodating a seapage of fluid past the pressure balancing seals while maintaining the pressure balancing feature, determining when the first environmental seal fails, and estimating the life of the back up environmental seal.
Another object of this invention is to provide a motion compensator including means for lubricating its environmental seals during the operation of the compensator which is an improvement over the motion compensator as claimed in the aforementioned application of George M. Raulins.
These and other objects, features, and advantages of this invention will become apparent from the drawings, the detailed description and the appended claims.